{"id":66293,"date":"2019-10-31T10:22:19","date_gmt":"2019-10-31T17:22:19","guid":{"rendered":"https:\/\/www.racingjunk.com\/news\/?p=66293"},"modified":"2019-10-31T10:22:19","modified_gmt":"2019-10-31T17:22:19","slug":"what-are-the-differences-in-big-holley-4150-carburetors-part-4","status":"publish","type":"post","link":"https:\/\/www.racingjunk.com\/news\/what-are-the-differences-in-big-holley-4150-carburetors-part-4\/","title":{"rendered":"What are the Differences in Big Holley 4150 Carburetors? Part 4"},"content":{"rendered":"<p class=\"jetpack-slideshow-noscript robots-nocontent\">This slideshow requires JavaScript.<\/p><div id=\"gallery-66293-1-slideshow\" class=\"jetpack-slideshow-window jetpack-slideshow jetpack-slideshow-black\" data-trans=\"fade\" data-autostart=\"1\" data-gallery=\"[{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C1-3.jpg&quot;,&quot;id&quot;:&quot;66294&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;Over the past several weeks, we looked at three very different Holley carburetors \\u2013 a Classic Double Pumper, an HP-series model and one of the newest XP-series examples. All are double pumper configurations and while each share similarities, they also have different components and features. To conclude the series, we\\u2019ll remove the bowls and metering blocks and look inside. The differences are plentiful.\\n\\nBoth the Classic Double Pumper and the HP carbs use cast metering blocks. Meanwhile, the XP series incorporates billet aluminum blocks. The Classic double pumper and HP blocks are similar, but with a different layout. For example, the Classic block is set up with a vacuum port. This is a timed spark port (it provides no vacuum at curb idle). None exist in the HP. The XP, however, is a different story:\\n\\nOpen up an XP carb and you\\u2019ll quickly discover they\\u2019re pretty much tunable for anything. Aside from the standard replaceable jets and power valves, the metering blocks allow for tuning the idle fed restrictions, emulsion bleed restrictors and the power valve channels. Holley determines the idle circuit calibration by the diameter of the idle feed restriction (IFR) coupled with the idle air bleed. The pair of idle feed restrictors is nothing more than a jet for the idle system while the air bleed serves as the airflow-regulating orifice. Holley also notes that by turning the idle mixture screw(s), you vary the volume of air\\\/fuel emulsion discharged into the intake manifold, not the actual air\\\/fuel ratio. Given the new design of the metering block, it\\u2019s possible to change the idle feed restrictor size to compensate for a large (big duration, high overlap) camshaft. With a combination such as this, the intake charge is often diluted at idle. The dilution is created because the intake charge is pulled out the header due to a late closing exhaust valve. To bring back idle quality (and sensitivity) to the idle mixture screws, the idle feed restriction size must be increased.\\n\\nHolley also includes power valve channel restrictions in each metering block. There are two restrictions, visible when the power valve is removed. These restrictions meter the flow of fuel into the main carburetor well. It is the diameter of these restrictions that dictates the amount of fuel that goes into the circuit. When the size of the restriction is changed, the air\\\/fuel ratio will change at wide-open throttle (full power). When the power valve is closed at idle or at part throttle, the power valve restrictions will obviously have no effect.\\n\\nIn total, there are ten emulsion bleeds on each metering block. Emulsion bleeds can have an effect upon power, but this is highly dependent upon the engine combination. If you wish to tune by way of emulsion bleeds, it must be done on a dynamometer where you can carefully monitor the air\\\/fuel ratio. Holley offers a wide selection of emulsion bleed tuning components, ranging from a twenty-bleed kit to emulsion bleed two-packs. \\n\\nFinally, when you consider the wear and tear on a set of metering blocks (particularly in a race application), you can see the use of a billet aluminum block is a great addition. Sealing is improved, too. Holley also added a handy pry slot on each block for easier disassembly. \\n\\nLook inside the bowls and you\\u2019ll also find some differences. The Classic Double Pumper has a brass float bowl. The HP series carburetor comes with a nitrophyl float. The XP also uses a nitrophyl float assembly. Here, the floats are notched on both sides for jet extensions. We\\u2019ve mentioned this before, but the HP can be plumbed for fuel on either (or both) of the carburetor\\u2019s sides. Ditto with the XP. The XP has a slightly larger bowl capacity, and internally, the bowl is engineered with special fuel \\u201ctrough\\u201d that directs fuel to the jets.\\n\\nAs you can see, there are a lot of differences (and similarities) between the three Holley double pumper carbs. The Classic is still a great street carburetor. The HP balances between hard core street and strip and the XP is an outstanding race fuel mixer. For more info, check out the accompanying photo slideshow.&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C36.jpg&quot;,&quot;id&quot;:&quot;66295&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 1&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;The metering blocks on the Classic Double Pumper and the HP series carb are similar (Classic Double Pumper on the left).&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C37.jpg&quot;,&quot;id&quot;:&quot;66296&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 2&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;One place where they differ is the lack of a vacuum port on the HP series carb. This is a timed spark port on the Double Pumper.&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C38.jpg&quot;,&quot;id&quot;:&quot;66297&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 3&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;Metering blocks are billet aluminum on the XP series carburetor, and they\\u2019re designed for maximum adjustment capability.&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C39.jpg&quot;,&quot;id&quot;:&quot;66298&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 4&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;In this photo, you can see the replaceable emulsion bleeds found on the XP.&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C40.jpg&quot;,&quot;id&quot;:&quot;66299&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 5&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;The pointer locates the replaceable idle feed restrictor on the XP.&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C41.jpg&quot;,&quot;id&quot;:&quot;66300&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 6&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;This photo shows the pair of replaceable power valve restrictors (they\\u2019re visible once the power valve is removed). The text offers more info on the adjustment capability found within the metering blocks. It\\u2019s considerable.&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C42.jpg&quot;,&quot;id&quot;:&quot;66301&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 7&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;Bowls used on the Classic Double Pumper and the HP are similar; however, the XP (not shown here) bowls have increased capacity.&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C43.jpg&quot;,&quot;id&quot;:&quot;66302&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 8&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;The XP series carb also uses nitrophyl floats, and they\\u2019re notched. Holley designed a special fuel \\u201ctrough\\u201d within the bowl to direct fuel to the jets.&quot;,&quot;itemprop&quot;:&quot;image&quot;},{&quot;src&quot;:&quot;https:\\\/\\\/www.racingjunk.com\\\/news\\\/wp-content\\\/uploads\\\/2019\\\/10\\\/C44.jpg&quot;,&quot;id&quot;:&quot;66303&quot;,&quot;title&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4 9&quot;,&quot;alt&quot;:&quot;What are the Differences in Big Holley 4150 Carburetors? Part 4&quot;,&quot;caption&quot;:&quot;The notch on the rear float allows you to use a set of jet extensions, which are included with the carburetor.&quot;,&quot;itemprop&quot;:&quot;image&quot;}]\" itemscope itemtype=\"https:\/\/schema.org\/ImageGallery\"><\/div>\n","protected":false},"excerpt":{"rendered":"<div class=\"mh-excerpt\"><p>To conclude this series, we\u2019ll remove the bowls and metering blocks from these carbs and look inside.<\/p>\n<\/div>","protected":false},"author":20,"featured_media":66294,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[5028,3697,11,3470,4879],"tags":[1076,4892,15,3611,2468,41,4888,321],"class_list":["post-66293","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-fuel-delivery","category-galleries","category-how-tos","category-news","category-slideshow","tag-carburetors","tag-galleries","tag-holley","tag-holley-carb","tag-holley-carburetor","tag-news","tag-slideshow","tag-wayne-scraba"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/www.racingjunk.com\/news\/wp-content\/uploads\/2019\/10\/C1-3.jpg","jetpack_shortlink":"https:\/\/wp.me\/p42YSK-hff","jetpack_sharing_enabled":true,"amp_enabled":true,"_links":{"self":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/66293","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/users\/20"}],"replies":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/comments?post=66293"}],"version-history":[{"count":1,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/66293\/revisions"}],"predecessor-version":[{"id":66304,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/66293\/revisions\/66304"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/media\/66294"}],"wp:attachment":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/media?parent=66293"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/categories?post=66293"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/tags?post=66293"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}